A RLC protocol layer is a sub-layer of Layer 2 (L2) in a radio interface protocol stack of the LTE, and is located between a Media Access Control (MAC) layer and a Packet Data Convergence Protocol (PDCP) layer. Functions of the RLC protocol layer include link control, packaging and reassembly, concatenation, user data transmission, error correction, protocol error detection and repair etc., which provides segmentation and retransmission services for users and control data.
Each RLC protocol entity is configured by a Radio Resource Control (RRC) layer and operates in three data transmission modes, which are a Transparent Mode (TM), an Unacknowledged Mode (UM) and an Acknowledged Mode (AM) respectively. In the Automatic Repeat Request (ARQ) in the AM, the reliability of data transmission is ensured by a receiving end transmits a status report to a transmitting end, and the transmitting end determining which Protocol Data Units (PDUs) have been acknowledged to be received by the receiving end and which PDUs or PDU segments require retransmitting according to a packet number (ACK_SN) where the status report cuts off (ACK_SN) in the status report and packet numbers (NACK_SN) of packets which are not received before the ACK_SN. FIG. 1 is a schematic diagram of architecture of a RLC in an AM protocol.
In the 36.322 protocol, at present, the process for triggering a status report in the AM involves two timers, both of which are used in a RLC data transmission receiving end. The first one is a reordering timer (t-Reordering), which is used to detect a loss condition of bottom layer data, and a status report is transmitted to a transmitting end when the t-Reordering is timeout. The second one is a status prohibiting timer (t-StatusProhibit), which is used to limit a frequency at which the status report is transmitted, i.e., the time for twice transmitting the status report should satisfy a certain time interval. There are two modes for triggering the status report: 1) the RLC transmitting end performing the triggering in a polling mode; and 2) the RLC receiving end detecting that the reception of the PDU fails (the t-Reordering is timeout). The second mode related to the present invention will be described primarily here. First, if the RLC receiving end detects that the packets do not arrive in order, the RLC receiving end will enable the t-Reordering immediately, and when the t-Reordering is timeout, update of the VR(MS) and transmission of the status report will be triggered, wherein the VR(MS) is used to identify and a cut-off location of the constructed status report in a data receiving window, i.e., a value of the above ACK_SN, and the transmission of the status report must be triggered after the update of the VR(MS). Second, the triggering of the status report is not unlimited at all, but is required to satisfy a certain transmission interval. If the t-StatusProhibit does not operate, and when the first transmission occasion indicated by a lower layer arrives, a status report will be constructed and delivered to the lower layer; otherwise, when the first transmission occasion indicated by the lower layer arrives after the t-StatusProhibit is timeout, a status report will be constructed and delivered to the lower layer. When one status report has been delivered to the lower layer, a receiving side of the RLC AM entity will enable the t_status_prohibit timer.
It can be seen from the above discussion that the transmission of a packet in the AM should be acknowledged by a status report. As a Hybrid Automatic Repeat Request (HARQ) of the bottom layer has a limitation on the number of times for retransmitting the loss packets, there is no mechanism for ensuring that the status report per se will be received certainly at the RLC layer, and the twice triggering of the status report are required to satisfy a certain time interval. Thus, if the status report is lost at the bottom layer, that is, the packet retransmission of the status report is unsuccessful, the retransmission will be implemented only when the status report is triggered at the next time.
However, in certain conditions of the AM, the acknowledgement of the status report by an upper layer is necessary, which is primarily represented in the condition that the receiving window is about to be filled up. When the receiving window stops, the transmitting window also necessarily has stopped. At this time, if the data receiving end triggers the status reports but the status reports is lost at the lower layer, the transmitting end is requested to retransmit the corresponding PDU segments only when a new round of status reports are triggered.
In the related art, no matter the method for triggering a status report is in which data transmission window status, the status report constructed at each time is only transmitted once, and it cannot ensure that the status report is transmitted to a data transmitting end successfully, so that is cannot ensure that the status report can trigger an effective packet retransmission, which may lead to relieving the stopped status of the window only if it is needed to wait for at least one period of the status prohibit timer or the reordering timer or a polling timer in the condition that the window stops due to being filled up. Therefore, it causes that the transmission of air interface data is delayed and the transmission speed of air interface data is relatively low.